Kevin is 40 years old and Ben is 10 years old. How many years will it take until Kevin is only 3 times as old as Ben?
Answer: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Kevin will be $40 + y$ years old and Ben will be $10 + y$ years old. At that time, Kevin will be 3 times as old as Ben. Writing this information as an equation, we get: $40 + y = 3 (10 + y)$ Simplifying the right side of this equation, we get: $40 + y = 30 + 3 y$ Solving for $y$ , we get: $2 y = 10$ $y = 5$.